Background We investigated race–ethnic and sex‐specific relationships of left ventricular ( LV ) structure and LV function in African American and white men and women at 43 to 55 years of age. Methods and Results The Coronary Artery Risk Development in Young Adults ( CARDIA ) Study enrolled African American and white adults, age 18 to 30 years, from 4 US field centers in 1985–1986 (Year‐0) who have been followed prospectively. We included participants with echocardiographic assessment at the Year‐25 examination (n=3320; 44% men, 46% African American). The end points of LV structure and function were assessed using conventional echocardiography and speckle‐tracking echocardiography. In the multivariable models, we used, in addition to race–ethnic and gender terms, demographic (age, physical activity, and educational level) and cardiovascular risk variables (body mass index, systolic blood pressure, diastolic blood pressure, heart rate, presence of diabetes, use of antihypertensive medications, number of cigarettes/day) at Year‐0 and ‐25 examinations as independent predictors of echocardiographic outcomes at the Year‐25 examination ( LV end‐diastolic volume [ LVEDV ]/height, LV end‐systolic volume [ LVESV ]/height, LV mass [ LVM ]/height, and LVM / LVEDV ratio for LV structural indices; LV ejection fraction [ LVEF ], Ell, and Ecc for systolic indices; and early diastolic and atrial ratio, mitral annulus early peak velocity, ratio of mitral early peak velocity/mitral annulus early peak velocity; ratio, left atrial volume/height, longitudinal peak early diastolic strain rate, and circumferential peak early diastolic strain rate for diastolic indices). Compared with women, African American and white men had greater LV volume and LV mass ( P <0.05). For LV systolic function, African American men had the lowest LVEF as well as longitudinal (Ell) and circumferential (Ecc) strain indices among the 4 sex/race–ethnic groups ( P <0.05). For LV diastolic function, African American men and women had larger left atrial volumes; African American men had the lowest values of Ell and Ecc for diastolic strain rate ( P <0.05). These race/sex differences in LV structure and LV function persisted after adjustment. Conclusions African American men have greater LV size and lower LV systolic and diastolic function compared to African American women and to white men and women. The reasons for these racial‐ethnic differences are partially but not completely explained by established cardiovascular risk factors.